Dealing with missing values

[jeroen]

There is a big bug in the current version of crossfilter, which causes missing values to be filled in with some random value. See here for an example: http://jsfiddle.net/VgvCB/

@jasondavies fixed this in a branch (see square/crossfilter#3 ) which will hopefully make its way into the master branch soon. For dc.js this means that it should expect the crossfilter grouping to return an additional key-value pair for which the key is null. See here for an example: http://jsfiddle.net/Cr44L/3/.

Perhaps dc should introduce an option for e.g. pie-charts if the null group should be displayed as a separate pie-slice, or if it should be ignored all together. The safest default for all charts is probably to not display the null group?

[NickQiZhu]

Interesting, will definitely do some research on that. The defaults recommended by you sound resonable, will create some test cases to verify this. Hopefully can get this in v1.2 release.

[jeroen]

Cool! I would suggest using Jason's branch until it is merged into the official crossfilter master.

[NickQiZhu]

Now I am considering introducing a driver concept to give user full control how crossfilter can be used, also making it possible to support plain series as well as other data mining library. Will try to do it in v1.3 release.

[jrideout]

The crossfilter bug has been addressed. We still might want to tackle this for Nick's non-crossfilter plans, but can track that in another issue.